Photoacoustic imaging (PAI) is used as a tool to investigate endogenous tissue components. In PAI, non-ionizing laser pulses are delivered into endogenous tissues; some of the delivered energy is absorbed and converted into heat, leading to thermoelastic expansion and consequent ultrasonic emission. The generated ultrasonic waves are then typically detected by ultrasonic transducers and are used to form images.
The absorption of the delivered energy in endogenous tissues can be due to molecules such as hemoglobin, for example. PAI thus provides a unique ability to image hemodynamics within microcirculatory tissue beds in vivo.
Current photoacoustic microscopy employs a confocal configuration to achieve imaging with optical-resolution for endogenous tissues with a maximal penetration depth of approximately 1.0 mm. Because of the strong attenuation of ultrasound waves in air, acoustic coupling (i.e., physical contact) between a sample and an acoustic transducer is typically required for ultrasound detection. This requirement can make photoacoustic imaging of biological samples difficult, limiting its practical applicability.
There is a need for a method and system for noncontact PAI that provides stable photoacoustic detection for imaging a sample.